1. Field of the Invention
The present invention relates to an image pickup device, and more particularly to an image pickup device having a function for performing a process to correct the magnification chromatic aberration of an acquired image.
2. Description of the Related Art
In recent years and continuing, there are growing demands for wide-angle image pickup devices, such as those used as back monitors of vehicles. However, as the angle becomes wider, magnification chromatic aberration and distortion aberration increase. As a result, it will be difficult to design an optical system having small aberration. For this reason, the performance needs to be improved by combining image processing with the image pickup operation.
In the conventional technology, there are methods for correcting the aberration of an image device including an optical system having magnification chromatic aberration and distortion aberration. One example is a method of converting the coordinates of R (red), G (green), and B (blue) signals acquired with an image sensor such as a CCD or a CMOS sensor, which conversion is performed separately for each of the RGB components in subsequent stages. Accordingly, magnification chromatic aberration and distortion aberration are simultaneously corrected. In another method, the magnification chromatic aberration is ignored, and only the distortion aberration is corrected by having the coordinates of the RGB components converted together (see, for example, patent document 1). In this method, the coordinate conversion parameters are fixed.
Patent Document 1: Japanese Laid-Open Patent Application No. 2006-345054
In an image pickup device including an aberration correction process function, magnification chromatic aberration correction is performed on an image taken with an optical system having large magnification chromatic aberration. However, there have been cases where the image quality becomes degraded as a result of performing the magnification chromatic aberration correction, which is counter to the intended effect. For example, in the case of an in-vehicle camera, when the vehicle enters a tunnel, and the light sources in the tunnel are natrium lamps, the image quality becomes degraded as a result of the magnification chromatic aberration correction, which is counter to the intended effect. The same results are seen when various lights of the vehicle are turned on/off.
This is because the light sources (illumination lights) have different wavelength distributions (spectral). Accordingly, when the coordinate conversion parameter for the magnification chromatic aberration is set in correspondence with one of the wavelength distributions, and then the light changes to another light, the colors in the image may become blurred. Thus, to achieve images of higher quality when performing magnification chromatic aberration correction, the coordinate conversion parameter for the magnification chromatic aberration correction needs to be changed in accordance with the spectral of the illumination light. However, in the conventional technology, the coordinate conversion parameter is fixed, and therefore when the light source or the illumination light changes, the image quality inevitably becomes degraded as a result of the magnification chromatic aberration correction, which is counter to the intended effect.